What is the difference between "P-Asserted-Identity" and "P-Called-Party-ID"?

Question

Please explain the scenario with an example which has both the ids are different in a single SIP session.

Along with it also explain in IMS network who fills the "P-Called-Party-ID" (is it P-CSCF / S-CSCF session manager).

Answer 1

In short:

• P-Asserted-Identity is the address of who initiated the call from the point of view of the SIP server - aka the caller. This is in many cases the same as the address in the "From" header, but can be different if the caller has many identities to reflect the relevant one for the destination. An example will be a call from [email protected] to PSTN, the P-Asserted-Identity can be set to the telephone number associated with "alice".
• P-Called-Party-ID is the address of who was called from the point of view of the SIP server - aka the callee. Typically this is the address in request URI (R-URI) of the incoming request to the SIP server. This is useful because the SIP server can change the R-URI (e.g. to be the IP:PORT of the device based on the Contact address of the associated registration).